Synchronously operating circuit breaker with improved circuit breaker operating mechanism

ABSTRACT

A circuit breaker has normally closed main contacts and normally open secondary or synchronous contacts. For low current interruption, the main contacts open the circuit. When a high fault current occurs, the secondary contacts are closed before the main contacts are opened. The secondary contacts are then opened just prior to a current zero after the opening of the main contacts. The secondary contacts are operated by hydraulic means having a driving piston actuated by the same mechanism which operates the main contacts and a puffer piston. Sliding valves and repulsion coil actuated valves in the hydraulic means cooperate to control the operation of the driven piston, which operates the moving secondary synchronous contact. The energerization of the repulsion coils is controlled by currentresponsive means and a synchronous control device. A synchronous operator controls a valve to direct the flow of gas from the puffer to either the main or the secondary contacts.

United States Patent Circle [54] SYNCHRONOUSLY OPERATING CIRCUIT BREAKER WITH IMPROVED CIRCUIT BREAKER OPERATING MECHANISM [72] Inventor: Robert Ray Circle, Woodbridge, Va.

[73] Assignee: Westinghouse Electric Corporation, Pittsburgh, Pa.

[22] Filed: Feb. 19, 1970 [21] Appl. No.: 12,713

[15] 3,655,931 [451 Apr. 11,1972

FOREIGN PATENTS OR APPLICATIONS 1,083,897 6/ I960 Germany ..200/82 R Primary Examiner-Robert K. Schaefer Assistant Examiner-Robert A. Vanderhye Attorney-A. T. Stratton, C. L. McHale and W. R. Crout [57] ABSTRACT v A circuit breaker has normally closed main contacts and normally open secondary or synchronous contacts. For low current interruption, the main contacts open the circuit. When a high fault current occurs, the secondary contacts are closed before the main contacts are opened. The secondary contacts are then opened just prior to a current zero after the opening of the main contacts. The secondary contacts are operated by hydraulic means having a driving piston actuated by the same mechanism which operates the main contacts and a puffer piston. Sliding valves and repulsion coil actuated valves in the hydraulic means cooperate to control the operation of the driven piston, which operates the moving secondary synchronous contact. The energerization of the repulsion coils is controlled by current-responsive means and a synchronous control device. A synchronous operator controls a valve to direct the flow of gas from the puffer to either the main or the secondary contacts.

16 Claims, 6 Drawing Figures HYDRAULIC FLUID OPERATING 2 MECHANISM I l I I I I I I I CLOSED POSITION Patented April 11, 1972 3,655,931

5 Sheets-Sheet l FIG I CLOSED posmow MECHANISM OPERATING HYDRAULIC 8| INVENTOR Robert R. Circle S? 4 BY 2 LL 8 f W 01/36 ATTORNEY Patented April 11, 1972 5 Sheets-Sheet 2 Patented April 11, 1972 5 Sheets-Sheet 3 Patented April 11, 1972 5 Sheets-Sheet 4 Am3OZOmI02 wv 202 Patented April 11, 1972 5 Sheets-Sheet 5 ZOTCmOQ E3050 zmmo jDu mdE SYNCHRONOUSLY OPERATING CIRCUIT BREAKER WITH IMPROVED CIRCUIT BREAKER OPERATING MECHANISM BACKGROUND OF THE INVENTION This invention relates, generally, to synchronous circuit breakers and to circuit breaker operating mechanisms and, more particularly, to hydraulic mechanisms for operating circuit breakers having synchronously operated contacts, which are opened just prior to a current zero of an alternating current wave.

In a copending application, Ser. No. 435,557, filed Feb. 26, 1965, now US. Pat. No. 3,390.240, issued June 25, 1968 to Robert R. Circle and T. O. Prunty, and assigned to the Westinghouse Electric Corporation, there is described a circuit breaker having main or nonsynchronous contacts and secondary or synchronous contacts, which are connected in parallel-circuit relation when the breaker is closed. The main contacts normally carry most of the current since they are of a heavier construction and provide a shorter path having a low voltage drop through the breaker. When the breaker begins to open, all of the current is shunted through the secondary contacts, which are opened just prior to a current zero by gas pressure developed by a puffer and controlled by a valve operated by a synchronous operator. The same puffer supplies gas to extinguish the arc drawn either at the synchronous contacts, which interrupt high-fault currents, or at the nonsynchronous contacts, which interrupt currents too low to operate the synchronous operator.

SUMMARY OF THE INVENTION In accordance with the present invention, the synchronous or secondary contacts of a circuit breaker are operated by hydraulic means having a driving piston actuated by the same mechanism which operates the main contacts and a puffer piston. The main contacts are normally closed and the secondary contacts are normally open. For load break switching and low current interruption, the main contacts open the circuit. When a high fault current occurs, the secondary contacts are closed before the main contacts are opened. The secondary contacts are then opened just prior to a current zero after the opening of the main contacts. Sliding valves and repulsion coil actuated valves in the hydraulic mechanism cooperate to control the operation of the driven piston which operates the moving secondary synchronous contact. The energization of the repulsion coils is controlled by current responsive means and by a synchronous control device. A synchronous operator controls a valve to direct the flow of gas from the puffer to either the main or to the secondary contacts.

BRIEF DESCRIPTION OF THE DRAWING For a better understanding of the nature of the invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a diagrammatic view of a circuit breaker and hydraulic operating mechanism embodying principal features of the invention with the main contacts in the closed position and the secondary synchronous contacts open;

FIG. 2 is a view, similar to FIG. 1, with the main and secondary contacts in their respective positions during fault current conditions;

FIG. 3 is a view, similar to FIG. 1, with the contacts in their respective positions during fault current interruption;

FIG. 4 is a view, similar to FIG. 1, showing the contacts in their respective positions during the load break (nonsynchronous) switching;

FIG. 5 is a view, similar to FIG. 1, with the contacts in their fully open circuit positions; and

FIG. 6 is a diagrammatic view of a synchronous control device utilized with the mechanism shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, and particularly to FIG. 1, the circuit breaker shown therein is of the general type described in the aforesaid copending application. Ser. No. 435,557 now US. Pat. No. 3,390,240, issued June 25, 1968. The circuit breaker structure comprises a housing 10, terminal bushings 11 and 12 mounted upon the housing 10, main nonsynchronous contact means 13, secondary synchronous contact means 14, puffer means 15, a synchronous operator 16 for operating a valve 17, and a mechanical linkage 18 interconnecting the puffer means 15 and a movable main nonsynchronous contact member 19, and also a hydraulic means 20 for operating the secondary contact means 14. The housing or tank 10 contains an interrupting gas, preferably sulfur hexafluoride (SF gas, at a relatively low pressure. Other interrupting gases, such as air, may be utilized, if desired The main contact means 13 includes a relatively stationary contact finger assembly 21, an orifice member 22 having an arcing ring 23 disposed in a generally cylindrical throat 24 of the orifice member, the generally cylindrical movable contact member 19, which passes through the throat 24 to engage the base of a generally cup-shaped member 25 movably disposed in the finger assembly 21, a contact finger assembly 26 slidably engaging the movable contact member 19, and an insulating member 27 having one end attached to the movable member 19 and the other end connected to the mechanical linkage 18. The finger assembly 26 is mounted in an insulating body member 28, and the assembly 26 is electrically connected through a conductor 40 to a portion 29 of the terminal bushing 12. The cup-shaped member 25 is biased outwardly in the finger assembly 21 by a compression spring 31. The finger assembly 21 is electrically connected to the primary winding of a coupling transformer 30 and also to a conductor 32. The primary of the transformer 30 is connected to a portion 33 of the terminal bushing 11.

The main contact members are of a relatively heavy construction. Thus, when the movable contact member 19 is closed to engage the member 25 and then the fingers 21, a current path having a relatively low resistance and low voltage drop is provided through the circuit breaker from the terminal bushing 11 to the terminal bushing 12. The bushings 11 and 12 may be connected to suitable power conductors.

The secondary contact means 14 includes a relatively stationary contact finger assembly 34 and a generally cylindrical movable synchronous contact member 35, which normally closes the entrance at one end of a hollow cylindrical metal flow director 36, to which the conductor 32 is connected. The finger assembly 34 is connected to the arcing ring 23 by a conductor 37. The movable member 35 is attached to an operating rod 38, to which a hydraulic piston 39 is attached. The hydraulic piston 39 is slidably disposed in a hydraulic cylinder 41, and is operated by the hydraulic mechanism 20, as will be described more fully hereinafter.

As explained hereinbefore, the secondary synchronous contact means 14 is normally open when the main contact means 13 is fully closed. Thus, the secondary contact means may be of a relatively light construction, since they do not carry the continuous or load current of the circuit breaker. However, when the main contact means is partly open, with the member 19 separated from the member 25, but still engaging the arcing ring 23, and the secondary contact means is closed, a circuit extends from the base of the finger assembly 21 through the conductor 32, the flow director or secondary stationary contact 36, the contact member 35, the finger assembly 34, the conductor 37, the arcing ring 23, the contact member 19 the finger assembly 26 and the conductor 40 which connects the base of the finger assembly 26 to the portion 29 of the terminal bushing 12. Thus, the secondary synchronous contact means carries the full amount of the current through the circuit breaker for a short time during an interrupting operation.

The pufier means 15 comprises a piston 42 slidably disposed in a cylindrical portion 43 of the main body member 28 and a piston rod 44, which may be driven by a suitable operating mechanism (not shown). The operating mechanism may be of a type well known in the art. When the circuit breaker is fully closed, the piston 42 if at the right hand end of the cylinder 43.

As shown, the mechanical linkage 18 comprises a lever 45 pivotally mounted on a fixed support 46, a link or links 47 which connect one end of the lever 45 to one end of the insulating member 27, and links 48 which connect the other end of the lever 45 to a projection 49 on the piston rod 44. The lever 45 may comprise two members which straddle the rod 44. Likewise, the links 47 and 48 may comprise two spaced members. Thus, the puffer and the main moving contact member 19 are so interconnected'that when the puffer piston 42 is driven in one direction to compress the interrupting gas, the main contact member 19 is driven in the opposite direction to be disengaged first from the contact finger assembly 21 and later from the arcing ring 23 at the member 19 moves towards its fully open position. The linkage mechanism 18 may be so constructed that the pufier piston 42 travels a greater distance and at a higher linear speed than the movable contact member 19, thereby providing a high gas pressure.

The synchronous operator 16 may be of the type fully described in a copending application, Ser. No. 97,656, filed Mar. 22, 1961, now U.S. Pat. No. 3,215,866, issued Nov. 2, 1965 to Fritz Kesselring and Lutz Seguin. As described in the aforesaid application, the synchronous operator 16 comprises a saturating magnetic core 51 having a plurality of air gaps therein and a moving coil or armature 52 rotatably mounted in a main air gap 53 and spring biased to the closed position by a torsion spring 50. The moving coil 52 comprises a winding closed upon itself and may consist, for example, of a rectangular copper or aluminum frame. The conductor 37 passes through a central opening 54 in the magnetic core 51. Thus, the core is energized by the current flowing through the conductor 37, which is the current to be interrupted by the secondary synchronous contact means 14 of the circuit breaker.

As described in the aforesaid U.S. Pat. No. 3,215,866, the core 51 unsaturates when the current decreases below a predetermined amount, and the rapid rate of change of flux in the core 51, which takes place as the current in the conductor 37 approaches zero, induces a secondary current in the annature coil 52, which reacts with the flux across the air gap 53 to produce a torque which rotates the armature coil 52. This torque is utilized to operate the valve 17, which is mounted on a shaft 55 of the armature 52. The valve 17 may be of the type fully described in a copending application Ser. No. 98,523, filed Mar. 27, 1961, now US. Pat. No. 3,215,804, issued Nov. 2, 1965 to Fritz Kesselring. Valves of other types may be utilized if desired.

The operator 16 may be so constructed that it will open the valve 17, which is held normally closed by the relatively light biasing spring 50, only at relatively large fault currents. Furthermore, the synchronous operator 16 may be constructed to open the valve 17 a short time, for example about 2 milliseconds, before a current zero. When the valve 17 is open, the gas compressed by the puffer 15 flows through a passageway 56 and out through the metal flow director 36 to interrupt any are drawn between the member 36 and the movable contact member 35 of the secondary synchronous contact means 14.

Should the synchronous interrupter fail to interrupt the current, the valve 17 will reclose immediately after current zero by a reversal of the torque provided by the synchronous operator l6, and the moving synchronous contact 35 will reclose in the manner described hereinafter. The valve 17 and the synchronous contact member 35 are both reopened at the next current zero. During this time, the throat 24 of the orifice 22 is closed by the member 19, thereby directing the gas flow through the passageway 56. Following a successful interruption, valve 17 will be returned to its closed position by the biasing spring 50.

If the current level is too low for the synchronous operator 16 to operate, the valve 17 will remain closed. Movement of the contact member 19 past the arcing ring 23 will open the throat 24 of the orifice 22, thereby permitting the compressed gas to flow from the puffer 15 through a passageway 57 and out through the throat 24 to interrupt any are drawn between the member 25 and the member 19 as shown in FIG. 4.

In addition to the piston 39 and the cylinder 41 previously mentioned, the hydraulic operating means 20 comprises a driving piston 61 slidably disposed in a cylinder 62, two slide valves 63 and 64 actuated by the piston rod 38 to open and close ports 68 and 66, respectively, an additional port 67 from a passageway 68 connecting the cylinder 41 with the cylinder 62 to form a closed hydraulic system, a piston rod 69 attached to the extension 49 on the rod 44 to actuate the piston 61, and two repulsion coil actuated valves 71 and 72. The valve 71 is biased to its open position by a spring 73 and closed by a repulsion coil 74. Likewise, the valve 72 is biased to its open position by a spring 75 and closed by a repulsion coil 76. The valve 71 closes an outlet 77 from the cylinder 41 into the passageway68 through the port 67. The valve 72 closes an outlet 78 from one end of the cylinder 41 into the passageway 68.

As previously stated, the piston rod 69 is attached to the extension 49 on the piston rod 44. Thus, the driving piston 61 of the hydraulic means 20 moves simultaneously with the puffer piston 42 and the main contact member 19 since they are interconnected by means of the linkage 18. The main contact member 19 may be closed by means of the external operating mechanism which drives the rod 44 to the right, thereby moving the puffer piston 42 and the hydraulic piston 61 to the right as shown in FIG. 1. When the piston 61 moves to the right, the hydraulic fluid is transferred from the right-hand side of the piston 61 through the passageways 68 and 78 into the cylinder 41 and out through the port 66 into the cylinder 62 at the left-hand side of the driving piston 61. Thus, the main non-synchronous contact means 13 may be closed without closing the secondary synchronous contact means 14.

As explained hereinbefore, for load break switching and low current interruption, the main current-carrying contacts 13 open the circuit. If a high fault current occurs, above some predetermined level, the synchronous or secondary synchronous contact means 14 are closed as the main contact member 19 starts moving. The breaker is so constructed that the secondary contact members make before the main contact members 13 break. The secondary contact members are closed by the hydraulic mechanism under the control of the valve 72. The repulsion coil 76 which actuates the valve 72 to its closed position is energized by the secondary winding of the coupling transformer 30, the primary winding of which is energized by the current flowing through the circuit breaker.

Auxiliary contact members 79 on the valve 72 and contact members 80 of a relay 81 are connected in series with the coil 76. The relay 81 functions to prevent the valve 72 from fluttering during normal load current. The actuating coil of the relay 81 is energized by a current transformer 82 disposed on the conductor 40, which carries the current flowing through the circuit breaker. The relay 81 may be constructed to close its contact members only when a predetermined amount of current is flowing through the circuit breaker.

Thus, the valve 72 is closed when the current flowing through the breaker exceeds a predetermined amount. The closing of the valve 72 stops the flow of hydraulic fluid from the left-hand side of the piston 61, which is now moving to the left in the cylinder 62, through the port 66 and out from the cylinder 41 through the outlet 78. The closing of the outlet 78 by the valve 72 causes pressure to be built up on the righthand side of the piston 39, thereby driving this piston to the left to close the secondary synchronous contact means 14. As the piston 39 moves to the left, the slide valve 64 closes the port 66, relieving the pressure on the piston 39. At the same time, the slide valve 63 uncovers the port 65, thereby permitting the hydraulic fluid to flow into the cylinder 41 and out through the port 67 past the valve 71 and through the outlet 77 into the passageway68 and the cylinder 62 at the righthand side of the piston 61. As the flow of fluid transfers, pressure is relieved from the valve 72 which is reopened under the influence of its biasing spring 75, the repulsion coil 76 having been deenergized by the opening of auxiliary contacts 79. The valves 71 and 72 may be constructed of a light metal, such as aluminum, to weigh only or grams. Thus, a slight impulse from the repulsion coil reduces the flow of fluid enough to cause the hydraulic pressure to force the valve to the fully closed position where it is retained until the pressure is relieved.

After the secondary synchronous contacts close, the main contacts separate and cause a rush of current through the synchronous operator 16 and a synchronous control device 85, both of which are energized by the current flowing through the conductor 37. As shown more clearly in FIG. 6, the synchronous control device 85 is of a saturating core reactor type and comprises a magnetic core 86 having an air gap 87 therein. A coil 88 is wound on the core 86. The rapid change of the flux in the core 86 caused by a change in the current flowing through the conductor 37 induces a current in the winding 88. The winding 88 is connected to the repulsion coil 74 on the valve 71 through conductors 89 in series with contact members of a position switch 91. The switch 91 functions to prevent the device 85 from causing the valve 71 to be closed at the initial rush of current through the secondary contact means 14 caused by the opening of the main contact means 13.

However, the valve 71 is closed just prior to a current zero after the closing of the secondary contact means. The synchronous control device 85 functions in a manner similar to the synchronous operator 16 to energize the repulsion coil 74 by the current induced in the winding 88 provided the contact members of the position switch 91 are closed. As shown, the switch 91 is actuated by a cam 92 on the rod 44, which moves simultaneously with the main contact member 19 and the driving piston 61 of the hydraulic mechanism. Thus, the cam 92 may be so located that the switch 91 is closed after the breaker current is transferred into the secondary contacts, and after the driving piston 61 attains sufficient velocity to impart kinetic energy to the hydraulic fluid, but with enough puffer and driving piston travel left to insure two synchronous operations at each of two successive current zeros.

The closing of the valve 71 prevents the flow of the hydraulic fluid from the cylinder 41 through the port 67 and outlet 77 into the passageway 68. This'causes pressure to build up in the cylinder 41 to drive the piston 39 to the right and open the secondary contact means 14. As the piston 39 moves to the right, the slide valve 63 closes the port 65 and the port 66 is opened by the slide valve 64, thereby transferring the flow of fluid to the right-hand side of the piston 39. If current continues to flow in conductor 37 after the current zero, the secondary synchronous contact means 14 is immediately reclosed by closing the valve 72 to stop the flow of fluid through the outlet 78. The secondary contact members are reopened at the next current zero under the control of the synchronous device 85 in the manner hereinbefore described. If the second attempt to interrupt is successful, the secondary interrupter 14 remains open; but failure to interrupt will again be followed by reclosure of the secondary contact means 14 as before. From the foregoing description, it is apparent that the invention provides a hydraulic means suitable for operating contact members of a circuit breaker under the control of a synchronous control device to open the contact members just prior to a current zero. The hydraulic means may be actuated by the same mechanism which operates the main contact members of the circuit breaker and a puiTer mechanism for the circuit'breaker. The hydraulic means provides positive and rapid operation of the secondary contact means.

I claim as my invention:

1. In a synchronous type circuit breaker, in combination, relatively movable main nonsynchronous contacts and relatively movable secondary synchronously actuated contacts,

said relatively movable secondary synchronously actuated contacts being open in the closed circuit position of the interrupter when the main contacts are closed, actuating means for operating the movable main nonsynchronous contacts, hydraulic means including a driving piston and a driven piston for operating the movable secondary synchronously actuated contacts, mechanical means interconnecting said actuating means and said driving piston, valve means for controlling the operation of the driven piston to open the secondary synchronous contacts while the main contacts are closed and only during the existence of high current conditions in the controlled circuit, and synchronous control means for controlling the operation of said valve means.

2. The synchronous type circuit breaker of claim 1, wherein the synchronous control means is energized by the current flowing through the secondary synchronously actuated contacts.

3. The synchronous type circuit breaker of claim 2, wherein the valve means is electrically operated and is controlled by the synchronous control means.

4. The synchronous type circuit breaker of claim 1, wherein pufier means are provided for compressing an interrupting gas, and the movable main contact and puffer means and the driving piston are operated simultaneously by the actuating means.

5. The synchronous type circuit breaker of claim 4, wherein the synchronous control means is responsive to the current flowing through the secondary synchronously actuated contacts.

6. The synchronous type circuit breaker of claim 4, wherein a valve is provided for directing the flow of gas from the puffer, and a synchronous operator energized by the current flowing through the secondary synchronously actuated contacts for operating the valve.

7. A synchronous type circuit breaker including a pair of cooperable contacts separable to establish an arc, hydraulic means for effecting the synchronous separation of said contacts including means defining a hydraulic operating cylinder having a hydraulic piston reciprocally movable therein; an operating rod mechanically interconnecting the hydraulic piston to one of the separable contacts to effect the opening and closing movements thereof, means defining an inlet port leading into said hydraulic cylinder on one side of the hydraulic piston, means defining an exhaust port leading out of the hydraulic cylinder on the same side of the hydraulic piston, means providing a flow of hydraulic fluid through the inlet port and out of the exhaust port on the same side of the hydraulic piston, a hydraulic valve controlling the flow of hydraulic fluid out of said exhaust port, and a synchronous operator responsive to the current condition of the breaker for controlling the closing of the hydraulic valve a predetermined time prior to a current zero on the alternating circuit wave, whereby the hydraulic piston will be caused to be opened and thereby effect the synchronous opening of the separable contacts.

8. The synchronous type circuit breaker of claim 7, wherein the synchronous operator is of the Kesselring type.

9. The synchronous type circuit breaker of claim 7, wherein a pair of main separable contacts are in electrical parallel to said first-mentioned pair of separable contacts.

10. The synchronous type circuit breaker of claim 7, wherein a second inlet port and a second exhaust port are provided on the other side of the hydraulic piston, and a second hydraulic valve controls the flow of fluid out of the second exhaust port.

11. The combination of claim 10, wherein electrical means responsive to the magnitude of the current passing through the circuit breaker controls the closing of the second hydraulic valve, whereby a closing operation of the contacts occur.

12. In a circuit breaker, in combination, relatively movable main contacts, relatively movable secondary contacts, actuating means for operating the movable main contact, hydraulic means for operating the movable secondary contact, said hydraulic means having a driving piston and a driven piston, mechanical means interconnecting said actuating means and said driving piston, valve means for controlling the operation of the driven piston to open the secondary contacts, synchronous control means for controlling the operation of said valve means, the synchronous control means being energized by the current flowing through the secondary contacts, and the valve means being actuated by a repulsion coil energized by the synchronous control means.

13. In a circuit breaker, in combination, relatively movable main contacts, relatively movable secondary contacts, actuating means for operating the movable main contact, hydraulic means for operating the movable secondary contact, said hydraulic means having a driving piston and a driven piston, mechanical means interconnecting said actuating means and said driving piston, valve means for controlling the operation of the driven piston to open the secondary contacts, synchronous control means for controlling the operation of said valve means, the secondary contacts being normally open when the main contacts are closed, additional valve means for controlling the operation of the driven piston to close the secondary contacts, and means responsive to the current flowing through the main contacts for controlling the operation of said additional valve means.

14. A circuit interrupter comprising main contact means, secondary contact means, actuating means for operating the main contact means, hydraulic means having a driven piston for operating the secondary contact means and a driving piston for operating the driven piston, said driving piston being operated by said actuating means, electrically operated valve means for controlling the operation of the driven piston, current-responsive means for controlling the operation of said electrically-operated valve means, and slide valve means actuated by the driven piston and cooperating with said electrically operated valve means to control the operation of the driven piston.

15. The circuit interrupter combination of claim 14, wherein additional electrically operated valve means are utilized which cooperate with the slide valve means to change the direction of movement of the driven piston while the driving piston continues to move in one direction.

16. The circuit interrupter combination of claim 15, wherein a synchronous device is utilized responsive to the current flowing through the secondary contact means for energizing the additional electrically operated valve means. 

1. In a synchronous type circuit breaker, in combination, relatively movable main nonsynchronous contacts and relatively movable secondary synchronously actuated contacts, said relatively movable secondary synchronously actuated contacts being open in the closed circuit position of the interrupter when the main contacts are closed, actuating means for operating the movable main nonsynchronous contacts, hydraulic means including a driving piston and a driven piston for operating the movable secondary synchronously actuated contacts, mechanical means interconnecting said actuating means and said driving piston, valve means for controlling the operation of the driven piston to open the secondary synchronous contacts while the main contacts are closed and only during the existence of high current conditions in the controlled circuit, and synchronous control means for controlling the operation of said valve means.
 2. The synchronous type circuit breaker of claim 1, wherein the synchronous control means is energized by the current flowing through the secondary synchronously actuated contacts.
 3. The synchronous type circuit breaker of claim 2, wherein the valve means is electrically operated and is controlled by the synchronous control means.
 4. The synchronous type circuit breaker of claim 1, wherein puffer means are provided for compressing an interrupting gas, and the movable main contact and puffer means and the driving piston are operated simultaneously by the actuating means.
 5. The synchronous type circuit breaker of claim 4, wherein the synchronous control means is responsive to the current flowing through the secondary synchronously actuated contacts.
 6. The synchronous type Circuit breaker of claim 4, wherein a valve is provided for directing the flow of gas from the puffer, and a synchronous operator energized by the current flowing through the secondary synchronously actuated contacts for operating the valve.
 7. A synchronous type circuit breaker including a pair of cooperable contacts separable to establish an arc, hydraulic means for effecting the synchronous separation of said contacts including means defining a hydraulic operating cylinder having a hydraulic piston reciprocally movable therein; an operating rod mechanically interconnecting the hydraulic piston to one of the separable contacts to effect the opening and closing movements thereof, means defining an inlet port leading into said hydraulic cylinder on one side of the hydraulic piston, means defining an exhaust port leading out of the hydraulic cylinder on the same side of the hydraulic piston, means providing a flow of hydraulic fluid through the inlet port and out of the exhaust port on the same side of the hydraulic piston, a hydraulic valve controlling the flow of hydraulic fluid out of said exhaust port, and a synchronous operator (85) responsive to the current condition of the breaker for controlling the closing of the hydraulic valve a predetermined time prior to a current zero on the alternating circuit wave, whereby the hydraulic piston will be caused to be opened and thereby effect the synchronous opening of the separable contacts.
 8. The synchronous type circuit breaker of claim 7, wherein the synchronous operator is of the Kesselring type.
 9. The synchronous type circuit breaker of claim 7, wherein a pair of main separable contacts are in electrical parallel to said first-mentioned pair of separable contacts.
 10. The synchronous type circuit breaker of claim 7, wherein a second inlet port and a second exhaust port are provided on the other side of the hydraulic piston, and a second hydraulic valve controls the flow of fluid out of the second exhaust port.
 11. The combination of claim 10, wherein electrical means responsive to the magnitude of the current passing through the circuit breaker controls the closing of the second hydraulic valve, whereby a closing operation of the contacts occur.
 12. In a circuit breaker, in combination, relatively movable main contacts, relatively movable secondary contacts, actuating means for operating the movable main contact, hydraulic means for operating the movable secondary contact, said hydraulic means having a driving piston and a driven piston, mechanical means interconnecting said actuating means and said driving piston, valve means for controlling the operation of the driven piston to open the secondary contacts, synchronous control means for controlling the operation of said valve means, the synchronous control means being energized by the current flowing through the secondary contacts, and the valve means being actuated by a repulsion coil energized by the synchronous control means.
 13. In a circuit breaker, in combination, relatively movable main contacts, relatively movable secondary contacts, actuating means for operating the movable main contact, hydraulic means for operating the movable secondary contact, said hydraulic means having a driving piston and a driven piston, mechanical means interconnecting said actuating means and said driving piston, valve means for controlling the operation of the driven piston to open the secondary contacts, synchronous control means for controlling the operation of said valve means, the secondary contacts being normally open when the main contacts are closed, additional valve means for controlling the operation of the driven piston to close the secondary contacts, and means responsive to the current flowing through the main contacts for controlling the operation of said additional valve means.
 14. A circuit interrupter comprising main contact means, secondary contact means, actuating means for operating the main contact means, hydraulic means haviNg a driven piston for operating the secondary contact means and a driving piston for operating the driven piston, said driving piston being operated by said actuating means, electrically operated valve means for controlling the operation of the driven piston, current-responsive means for controlling the operation of said electrically-operated valve means, and slide valve means actuated by the driven piston and cooperating with said electrically operated valve means to control the operation of the driven piston.
 15. The circuit interrupter combination of claim 14, wherein additional electrically operated valve means are utilized which cooperate with the slide valve means to change the direction of movement of the driven piston while the driving piston continues to move in one direction.
 16. The circuit interrupter combination of claim 15, wherein a synchronous device is utilized responsive to the current flowing through the secondary contact means for energizing the additional electrically operated valve means. 